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1.
Estimate of the driving force for creep crack growth
Otmar Kolednik, Marko Kegl, Nenad Gubeljak, Jožef Predan, 2025, original scientific article

Abstract: A discussion on the conventional creep crack growth parameters, e.g. the experimental C*-integral, C*exp, or the experimental Ct-integral, Ct,ssc, shows that the physical meaning of these parameters for growing cracks in elastic–plastic, creeping materials is not fully clear. Therefore, a comparison is presented in this paper between the conventional creep crack growth parameters, several J-integral related parameters and the crack driving force (CDF), which has been used in linear elastic and elastic–plastic fracture mechanics. The CDF for elastic–plastic, creeping materials is derived from basic thermodynamic principles and by applying the concept of configurational forces (CFs). A comprehensive numerical study is performed where crack propagation is modelled by alternating creep and crack extension steps at constant loads in a compact tension specimen made of the nickel-base superalloy Waspaloy at a temperature of 700 °C. The CDF is evaluated by a CF-based post-processing procedure after a conventional finite element computation. This procedure is applicable for small-scale creep (ssc-), transition creep (tc-) and “moderate” extensive creep (ec-) conditions. For more pronounced ec-conditions, the procedure might have to be adapted. It is shown that C*exp and Ct,ssc reflect the time derivative of the CDF during the creep stages. In contrast, the variations of the CDF coincide well with that of J-values estimated from the crack-tip opening displacement.
Keywords: fracture mechanics, creep crack growth, crack driving force, C*-integral, J-integral, configurational force concept, finite element method
Published in DKUM: 20.03.2025; Views: 0; Downloads: 5
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2.
Total Knee replacement with an uncemented porous tantalum tibia component: A failure analysis
Samo K. Fokter, Nenad Gubeljak, Esther Punzón Quijorna, Primož Pelicon, Mitja Kelemen, Primož Vavpetič, Jožef Predan, Luka Ferlič, Igor Novak, 2022, original scientific article

Abstract: Porous tantalum has been extensively used in orthopaedic surgery, including uncemented total knee arthroplasty (TKA). Favourable results were reported with earlier monobloc tibial components and the design evolved to modular implants. We aimed to analyse possible causes for extensive medial tibia bone loss, resulting in modular porous tantalum tibia baseplate fracture after primary TKA. Retrieved tissue samples were scanned with 3 MeV focused proton beam for Proton-Induced X-ray Emission (micro-PIXE) elemental analysis. Fractographic and microstructural analysis were performed by stereomicroscopy. A full 3D finite-element model was made for numerical analysis of stress–strain conditions of the tibial baseplate. Histological examination of tissue underneath the broken part of the tibial baseplate revealed dark-stained metal debris, which was confirmed by micro-PIXE to consist of tantalum and titanium. Fractographic analysis and tensile testing showed that the failure of the tibial baseplate fulfilled the criteria of a typical fatigue fracture. Microstructural analysis of the contact surface revealed signs of bone ingrowth in 22.5% of the surface only and was even less pronounced in the medial half of the tibial baseplate. Further studies are needed to confirm the responsibility of metal debris for an increased bone absorption leading to catastrophic tibial tray failure.
Keywords: total knee arthroplasty, uncemented, cementless, trabecular metal, porous tantalum, tibial component, cementless baseplate fracture
Published in DKUM: 20.03.2025; Views: 0; Downloads: 3
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3.
Monitoring surface state of AA7075-T6 during dynamic loading with FBG sensor
Marijana Milković, Matej Njegovec, Jožef Predan, Jure Javornik, Denis Đonlagić, Nenad Gubeljak, 2023, original scientific article

Abstract: The AA7075-T6 material is widely used in aerospace applications due to its favourable strength-to-weight ratio and cost-effectiveness. The material undergoes a process of cold rolling and subsequent stretching to form metal sheets. This process generates residual compressive stresses on the surface of the material. Surface changes in the material are observed at low stress levels, resulting in variations in residual stresses and surface roughness. This article presents an approach to monitor the surface state changes of AA7075-T6 material during dynamic loading using Fiber Bragg Grating (FBG) sensor. Numerical Finite Element Method (FEM) simulations analyse the transfer of deformations from the damaged surface through the adhesive layer to FBG with different cladding thicknesses. Loading induces microcrack-related intensity changes in the FBG optical spectrum and deformation response. The magnitude of the response is greater, when the cladding thickness of the optical fibre is thinner. Experimental results show that the FBG optical spectrum response varies with cumulative number of dynamic cycles.
Keywords: AA7075-T6, dynamic loading, Fiber Bragg Grating (FBG) sensor, surface condition
Published in DKUM: 10.03.2025; Views: 0; Downloads: 6
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4.
Dimenzioniranje premične čeljusti primeža za stiskalnico "Rotopress" : diplomsko delo
Nejc Lazar, 2024, undergraduate thesis

Abstract: V diplomskem delu je predstavljen postopek dimenzioniranja premične čeljusti primeža stiskalnice »Rotopress« za podjetje Ledinek Engineering d.o.o. Pri samem dimenzioniranju smo upoštevali, da je potrebno ohraniti vse pritrdilne površine, čeljust se ne sme plastično deformirati pri maksimalni delovni sili, ki znaša 200 kN, in pa sama konstrukcija mora biti enostavna za varjenje. Predstavili smo tri variante premične čeljusti in jih primerjali s staro verzijo, katere maksimalna delovna sila je bila 140 kN. Cilj je bil, da je na novi verziji premične čeljusti napram stari verziji zmanjšana masa konstrukcije, zmanjšana maksimalna napetost in pa pomik ne sme biti večji od 1 mm. Za potrebe varjenja smo določili tehnologijo varjenja in katere pozicije na konstrukciji je potrebno predhodno predgrevati. Izdelali smo tudi tehnično dokumentacijo.
Keywords: dimenzioniranje, premična čeljust, lameliran lepljen les, MKE, varjenje
Published in DKUM: 09.10.2024; Views: 0; Downloads: 29
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5.
Določanje faktorja intenzitete napetosti na razpoki, ki obdaja praznine v materialu : magistrsko delo
Marcel Prosen, 2024, master's thesis

Abstract: V magistrski nalogi smo obravnavali problematiko votline, ki je posledica nekovinskega vključka ali pore in razpoke v elementu. Obravnavali smo več različnih primerov, ki so imeli različne geometrijske kombinacije velikosti in lokacije votline, okrog katere je nastala razpoka. S pomočjo numeričnih simulacij smo ugotavljali, kakšna je razlika v enako veliki razpoki, ki je nastala iz votline, od ravninske do v materialu zajete razpoke. Razliko smo ugotavljali na osnovi numeričnih simulacij modela iz končnih elementov, na osnovi izračuna faktorja intenzitete napetosti vzdolž konture razpoke. Ugotovili smo, da pri kratkih razpokah, ki so nastale iz votline v materialu, so vrednosti faktorja intenzitete napetosti manjše, kot to velja za enako veliko ravninsko razpoko v notranjosti materiala. Rezultati so pomembni zaradi določanja relevantne vrednosti faktorja intenzitete napetosti po konturi razpoke, ki je nastala iz vključka, za določitev trajne dinamične trdnosti materiala.
Keywords: faktor intenzitete napetosti, razpoke, nekovinski vključki, pore, numerične simulacije, analitični preračuni
Published in DKUM: 04.09.2024; Views: 69; Downloads: 56
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7.
Topološka optimizacija rotorske lamele sinhronskega motorja s potopljenimi trajnimi magneti : magistrsko delo
Daniel Horvat, 2024, master's thesis

Abstract: Razvoj sodobnih pogonskih elektromotorjev na področju transporta predstavlja nove izzive. Potreba po doseganju visokih vrtljajev, navora in moči ob zagotovljenem dolgotrajnem obratovanju je prinesla k uporabi sinhronskih motorjev s potopljenimi trajnimi magneti. Magistrsko delo opisuje postopek topološke optimizacije rotorske lamele za omenjeni tip elektromotorjev, ki je potekal v programu CAESS ProTOp. Najbolj obremenjena območja rotorske lamele so mostički, ki morajo zadržati magnete pri vrtenju in zagotoviti mehansko stabilnost rotorja. Hkrati morajo biti dovolj tanki, da motor dosega potrebne elektromagnetne karakteristike. S topološko optimizacijo je bila pridobljena optimalna oblika mostičkov in manjša masa rotorske lamele. Rezultati topološke optimizacije so bili s pomočjo numeričnih simulacij v programu ANSYS primerjani z začetno, ročno optimizirano obliko rotorske lamele. Ugotovitve kažejo, da se s tanjšimi mostički optimalne oblike zmanjšajo napetosti in ekvivalentne plastične deformacije v kritičnih območjih. Uvedba sodobnih postopkov optimizacije v fazi razvoja lahko v prihodnosti zamenja proces ročnega iskanja optimalnih oblik in omogoči nov napredek na področju pogonskih elektromotorjev.
Keywords: topološka optimizacija, metoda končnih elementov, numerična simulacija, sinhronski motor s potopljenimi trajnimi magneti, CAESS ProTOp
Published in DKUM: 29.03.2024; Views: 284; Downloads: 0
.pdf Full text (9,17 MB)

8.
9.
Experimental study of crack propagation through cladded 316L/S355 steel produced by the hot-roll bonding process
Edvard Bjelajac, Andrej Skumavc, Fidan Smaili, Gorazd Lojen, Jožef Predan, Tomaž Vuherer, 2023, original scientific article

Abstract: A hot-rolled clad plate made of 316L stainless steel and S355 carbon steel was produced in a real industrial environment via GMAW welding, vacuuming, preheating to 1240 °C, and hot-roll bonding on four stand plate mills in nine passes with reduction rates between 20-6% per pass. The clad plates were solution annealed to achieve the usual delivery condition. Ultrasound testing showed a bonding rate of 100%. Metallographic examination revealed predominantly low concentrations of oxides at the interface. The tensile strength of the bond reached 155 MPa. The shear strength always satisfied the requirements of ASTM A264. It was observed that the concentration of oxide particles influenced the shear strength strongly. The lowest measured value was 172 MPa. Specimens notched in the base material and specimens notched in the clad layer were used in the Charpy impact test. In every case, only the notched layer broke, while the other layer was only bent. The absorbed energies were always higher than those of each material alone. Fracture mechanic tests gave similar results. The crack could not propagate from the notched layer into the other one, regardless of the material of the notched layer. Instead, delamination occurred. Due to delamination, K1c could not be determined, so KQ was given instead.
Keywords: clad plate, hot-roll bonding, shear strength, tensile strength, impact toughness, crack propagation
Published in DKUM: 28.03.2024; Views: 210; Downloads: 18
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10.
Parametrično modeliranje vrtljive mize polnilnega stroja : diplomsko delo
Luka Pihler, 2023, undergraduate thesis

Abstract: V diplomski nalogi bo predstavljeno parametrično modeliranje vrtljive mize polnilnega stroja v podjetju GEA Vipoll d.o.o. Kjer se ukvarjajo z izdelavo polnilnih linij za živilsko in prehrambeno industrijo, ki velja za eno pomembnejših industrij sveta. Predstavljena bo tudi polnilna linija na splošno in parametrično modeliranje, ki sem ga uporabil za modeliranje vrtljive mize. Celoten model in tudi tehnična dokumentacija sta bila narejena v paketu SolidWorks.
Keywords: vrtljiva miza, parametrično modeliranje, polnilni stroj
Published in DKUM: 22.01.2024; Views: 353; Downloads: 61
.pdf Full text (2,27 MB)

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